Field of the Invention
The present invention relates generally to bicycle components. More particularly, this invention relates to bicycle drive-train components. Still more particularly, this invention relates to a single pivot front derailleur and an optional dual-sided chain catcher that may be used with any front derailleur.
Description of Related Art
Most bicycles have multiple gears with front and rear derailleurs to change gears. A front derailleur is used to shift a bicycle chain between two or more chainrings of a crankset. A crankset typically includes two crank arms rotationally connected to a bottom bracket spindle at one end, and with pedals on opposite ends. Chainrings vary in diameter, each having a different number of teeth for engagement with the bicycle chain. The force required to turn the crankset is determined, in part, by the size of the particular chainring engaged by the bicycle chain. The size of the chainring can also determine the number of revolutions that will be required of the crankset in order to travel a certain distance. By changing the chain engagement from a chainring of one size to another, the bicyclist can strategically choose how much force will be required to be applied to the crankset, as well has how many revolutions the crankset will make in order to travel a relative distance.
Conventional bicycle frames are configured with a seat tube joined at one end to a down tube with a bottom bracket lug or shell. The bottom bracket lug supports the bottom bracket, typically consisting of the bottom bracket spindle, bearings, races, lock rings, spacers and the like, that are configured to couple with, and allow rotation of, the crankset. The opposite end of the seat tube conventionally supports a seat post and seat for the rider. A front derailleur is typically mounted on the seat tube of a bicycle frame and near the chainrings. Not all bicycle frames have a complete seat tube. For example, some full-suspension mountain bikes have a short seat tube stub for mounting a front derailleur that serves the purpose of a frame structural member for mounting the front derailleur. For simplicity of discussion, it will be assumed that the term, seat tube, denotes a full conventional seat tube or some other frame member, e.g., a short seat tube stub, for mounting the front derailleur.
A crankset attaches to opposite ends of a bottom bracket spindle. One arm of the crankset is simply a crank arm with a pedal designed to rotationally engage the bottom bracket spindle. The other arm of the crankset may include up to 3 chainrings supported on a crank arm spider to which a second pedal is attached. A front derailleur is necessary to shift the chain between the chainrings. The chainrings are typically arranged so as to be coaxial with, and parallel to, each other. The smallest chainring is typically closest to the bicycle frame with the chainrings progressively growing in diameter as they get further from the bike frame. The purpose of a conventional front derailleur is to urge the bicycle chain laterally away from the currently engaged chainring and towards a chainring selected by the rider through means of a properly connected shifting device also known as a shifter, typically using a derailleur cable under spring tension. Front derailleurs of various designs have been utilized to perform this function and most have similar features.
Construction and operation of a conventional front derailleur are described in U.S. Pat. No. 4,734,083 to Nagano. The Nagano front derailleur includes a member for fixing the front derailleur to the bicycle, a four pin linkage mechanism to effect a pantographic type movement of two guide members, the guide members typically being designated as the inner guide member and the outer guide member. When the assembly is activated to move away from the bicycle frame and toward a larger chainring, the inner guide pushes the bicycle chain laterally away from the bike frame until the bicycle chain leaves the currently engaged chainring and engages the next chainring. The action of urging the bicycle chain onto a larger chainring often involves the step of pressing the bicycle chain against the side of the larger chainring. By pressing the bicycle chain against the chainring, friction combines with the circular motion of the chainring to pull the bicycle chain up and onto the chainring. When the assembly is activated to move toward the bicycle frame and toward a smaller chainring, the outer guide urges the bicycle chain in a similar manner, with the outer guide pressing the bicycle chain off of the larger chainring, and then allowing the bicycle chain to fall onto the smaller chainring.
The inner and outer guides are spaced at a width which is wider than that of the bicycle chain, often one and a half to two times as wide as the bicycle chain. This allows the bicycle chain to run between the guides without contacting the guides while also allowing for some lateral movement of the bicycle chain which occurs when the bicycle chain is changed from one gear to another by a rear derailleur on a rear sprocket set also referred to as a cassette or cluster. The inner and outer guides each typically comprise a substantially flat elongated surface. The guides are placed substantially parallel to one another and are connected together with a front and rear link. An elongated spatial channel, often referred to as a cage is, thus, defined by the inner and outer guides and the front and rear links. The bicycle chain then passes through the cage without touching the inner and outer guides or the front and rear links during normal operation. There are typically multiple links of chain within the spatial area defined by the cage or chain guide at any given time.
It is possible for the bicycle chain to shift past the smallest inner chainring, especially when the inner chainring is very small. This can occur even on bikes adjusted by professional race mechanics. This inner chain derailment may result in the chain delivering no power to the rear wheel, or may get caught or tangled between moving parts, either of which is frustrating and potentially dangerous. Consequently, a small after-market of add-on products, called chain deflectors, exists to help prevent such inner derailments from occurring. Some of these conventional chain deflectors clamp around the seat tube, below the front derailleur, and at least one attaches to the front derailleur mount. However, such conventional chain deflectors do not appear to guard against an over-shift that would allow the chain to fall outside, or beyond the largest chainring.
The components of conventional front derailleurs may be constructed of any suitable materials, e.g., aluminum alloy, steel, plastic or carbon fiber composite. The pivot points used in links of the movement mechanism are usually bushings that generally require lubrication.
There are various cable pull types or configurations which can be used with shifting mechanisms of conventional front derailleurs to achieve movement of the chain guide. The bottom pull type is commonly used on road and touring bikes. The bottom pull type of derailleur is actuated by a cable pulling downwards relative to the location of the front derailleur. The cable in a bottom pull configuration is often routed across the top or along the bottom of the bottom bracket shell on a cable guide, which redirects the cable up the lower edge of the bicycle frame down tube. Full-suspension mountain bikes often have a bottom pull routing as the rear suspension hinders or prevents routing via the top tube of a bicycle frame.
The top pull cable configuration is more commonly seen on mountain bikes without rear-suspension. The front derailleur is actuated by a cable pulling upwards relative to the front derailleur, which is usually routed along the bicycle frame top tube, using cable stops and a short length of housing to change the cable's direction. This top pull configuration keeps the cable away from the underside of the bottom bracket and down tube which are subject to mud and dirt when off-road. Finally, there are some front derailleurs that are capable of either top pull or bottom pull and therefore can be used in either application.
Conventional front derailleurs are also capable of a couple different swing types depending on where the chain guide is mounted relative to the linkage or movement mechanism. In a bottom swing configuration, the derailleur chain guide is mounted to the bottom of the linkage mechanism, e.g., a four-link mechanism, which carries the chain guide. Alternatively, the front derailleur may be configured with a top swing configuration where the chain guide is mounted to the top of the movement mechanism. The top swing configuration was created as a way to get the frame clamp of the derailleur closer to the bottom bracket to be able to clear larger suspension components and allow different frame shapes. The compact construction of a top swing derailleur can cause it to be less robust than its bottom swing counterpart. Top swing front derailleurs are typically only used in applications where a bottom swing derailleur will not fit. And alternative solution would be to use an E-type front derailleur (discussed further below) which does not clamp around the seat tube at all.
Various approaches to securing a front derailleur to a bicycle frame member have been devised. The vast majority of front derailleurs are mounted to the frame by a clamp around the frame seat tube or its structural equivalent. Front derailleurs are available with several different clamp diameters designed to fit different types of frame tubing. Recently, there has been a trend to make front derailleurs with only one diameter clamp and then provide several sets of shims to space the clamp diameter down to the appropriate size of frame tubing.
An alternative to the clamp mounting mechanism is the braze-on derailleur hanger, where the front derailleur is mounted by bolting a tab on the front derailleur to a corresponding tab affixed to the bicycle frame seat tube by brazing, welding or other means. This braze-on mounting technique avoids any clamp size issues, but requires either a frame with the appropriate braze-on, or an adapter clamp that simulates a braze-on derailleur tab.
Alternatives to the clamp and braze-on mounting mechanisms include the E-type and direct-mount-derailleur (DMD) mounting mechanisms. The E-type front derailleur does not clamp around the frame seat tube, but rather is attached to the frame by a plate mounted under the drive side bottom bracket cup and a screw threaded into a boss on the seat tube. Such E-type front derailleur mounting mechanisms are usually found on mountain bikes with rear suspension components that do not allow space for a normal front derailleur clamp to go around the seat tube.
The DMD mounting mechanism, first introduced by Specialized Bicycles, employs a front derailleur bolted directly to bosses on a chainstay of the bicycle frame. The DMD configuration is typically used on dual suspension mountain bikes, where suspension movement causes changes to the chain angle as it enters the front derailleur cage. By utilizing a DMD system, the chain and derailleur move together during suspension travel, allowing for better shifting when the suspension is active.
Conventional chain guides, or front derailleur cages employ two parallel (inner and outer) plates that surround the bicycle chain and urge the chain laterally during shifting. The standard double cage type is intended to be used with cranksets having two chainrings. When viewed from the side, of the bicycle, the inner and outer plates of the double cage type have roughly the same profile. Alternatively, the alpine or triple cage type is used with front derailleurs designed to be used with triple cranksets having three chainrings, or with two chainrings that differ greatly in size (diameter). The alpine or triple cage type of chain guide employs a longer inner plate (relative to the outer plate) that extends further towards the bottom bracket's center of rotation. This longer inner plate helps to shift the chain from the smallest chainring onto the middle chainring more easily than with a standard double cage. In yet another approach to front derailleur cage design, U.S. Pat. Nos. 6,454,671 and 7,025,698 both to Christopher A. Wickliffe disclose annular chain guides.
In the evolution of front derailleurs, the conventional cable under spring tension with manual shift lever control has been replaced by electronic gear-shifting systems. An electronic gear-shifting system enables riders to shift with electronic switches instead of using conventional control levers. The switches are connected by electrical wire or wirelessly to a battery pack and to a small electric motor that drives the derailleur cage. However, such electronic gear-shifting systems generally employ the same four-link movement mechanism of most non-electronic shifting mechanisms.
Many conventional front derailleurs move a conventional chain guide, or derailleur cage, in an essentially lateral movement away from or toward the bicycle frame when shifting. On a properly adjusted front derailleur, the bicycle chain will only touch the chain guide during shifting. The chain guide is positioned by a movement mechanism, most commonly implemented using a four-link parallelogram mechanism to keep the chain guide properly aligned with the chain relative to the chainrings as the chain guide swings back and forth during shifting. There are usually two adjustment screws controlling the limits of lateral travel allowed. It is important to note that the conventional four-link, parallelogram mechanism moves the chain guide “laterally”, i.e., left to right and vice versa, between chainrings.
Alternatives to the conventional four-link movement mechanism for front derailleurs are known. For example, a front derailleur employing linear movement of a front derailleur chain guide has been disclosed in U.S. Pat. Nos. 6,454,671 and 7,025,698 both to Christopher A. Wickliffe. Additionally, a six-link front derailleur mechanism is disclosed in U.S. Pat. No. 8,303,443 to Wickliffe et al.
While all of these conventional front derailleurs are capable of adequately shifting a front derailleur, each has its drawbacks. Generally speaking, there is little vertical movement associated with conventional front derailleur shifting, especially of the four-link design, even though there may be significant vertical disparity between adjacent chainrings. Additionally, there is essentially no fore and aft movement of the derailleur cage or rotational movement of a derailleur cage of conventional front derailleurs. Finally, conventional front derailleurs tend to be complicated because of the many mechanical links involved in the movement mechanisms. Accordingly, an improved front derailleur mechanism which addresses at least some of these drawbacks of the prior art would be desirable.